"It's becoming a bigger problem than it ever had been before," Office of Traffic Safety spokesperson Chris Cochran said.
It's been suspected for a while but never quantified just for California until now. A new Office of Traffic Safety survey of nine cities during Friday and Saturday nights recently concluded more Californians are driving under the influence of drugs than alcohol -- more than double at 14 percent.
"Nearly half had marijuana, that was the drug; sometimes it was marijuana plus other drugs, or marijuana and alcohol," Cochran said.
Besides illegal drugs, the study also found people had prescription and over-the-counter drugs, which can impair driving.
The sleep aid Ambien has been linked to some high profile accidents. Low levels of the drug were found in the bloodstream of former U.S. Commerce Secretary John Bryson after a string of collisions in Southern California this summer. A few weeks later, Kerry Kennedy, daughter of Robert F. Kennedy, crashed north of New York City with the generic for Ambien in her blood. Neither case involved alcohol, backing the report's conclusion that drugged driving probably happens more often than drunk driving.
Mothers Against Drunk Driving recently added drugged driving to its campaign because of its rise.
"Driving under the influence no longer means alcohol, it includes alcohol and drugs and a combination of both," MADD California spokesperson Silas Miers said. "The result and consequences are the same. People get arrested or they end up dead."
Those advocating the recreational use of marijuana are not deterred by the report.
The Drug Policy Alliance opposes driving while impaired by pot but says California's numbers shouldn't prevent efforts to loosen up laws.
"No one should drive under the impairment of anything; I'm just saying the risks associated with marijuana and driving are substantially lower than the risks associated with alcohol and some prescription drugs," Drug Policy Alliance spokesperson Stephen Gutwillig said.
The state will have more concrete numbers in a few years because beginning in 2014, law enforcement will have to start indicating on DUI reports whether the case is related to alcohol, drugs or both.